Wetake red sandstone as the research object and apply the freeze-thawcycles

CT scans and mechanical properties experiments. We use image processingtechnology combined with genetic algorithm optimization model to achieve the denoise

enhancement

segmentation and three-dimensional reconstruction of CT scanimages after 0

5

10

20

and 40 freeze-thaw cycles. With the damageidentification and comparative study of the same object across scales

weestablished a prediction formula of elastic modulus deterioration based onmesoscopic damage. Therefore

the macroscopic mechanical behavior offreeze-thaw red sandstones can be interpreted from the physical nature of the materialmeso-structure. The results show that genetic algorithm based on imagemaximum entropy can quickly and accurately select the threshold for imagesegmentation

and achieve the recognition of matrix and defects in rock meso-structure.With the increase of freezing and thawing cycles

the porosity of rockincreases

and the fractal dimension of pore decreases. On the meso-scale

theevolution shows that the pores expand and the number increases

but thestructural complexity decreases. The macroscopic and mesoscopic damagevariables defined by the traditional methods are based on the effective bearingarea and elastic modulus

and they fail to fully consider the damage physicalmechanism and the internal structure information of the material. The damageevolution curves are different. Based on the two physical mechanisms

we definethe meso-damage variable and the macro-damage variable that considers the naturalrock damage

which achieves the combination of macroscopic and mesoscopic damages.Finally

according to the relationship between meso-structure evolution andmacroscopic mechanical response in the process of freeze-thaw cycles

wepropose a prediction formula of elastic modulus degradation

and analyze thedifferent dominant roles of pore size and pore structure morphology through thedamage process. We interpret the mechanical mechanism of macroscopic sandstonefreeze-thaw damage based on the meso-structure physical mechanisms.